The invention relates to a device making it possible to fix to a support at least one optical member with a relatively small thickness such as a filter, a mirror or a lens, particularly when the use conditions of said member lead to significant temperature variations. Such a fixing device can more particularly be used on an artificial infrared observation satellite for fixing filters equipping an infrared camera to a support.
As a result of the fragility or brittleness of the materials forming the filters (e.g. CdTe, germanium, silicon or CaF.sub.2), the conventional fixing devices cannot be used in an application of this type, because the mechanical and thermal stresses to which they are then exposed would lead to the filters becoming deformed or broken.
Thus, infrared observation requires working at a temperature equal to or below 100.degree. K. In view of the fact that the filters are fitted at ambient temperature, i.e. approximately 300.degree. K., the fixing device must subsequently withstand a temperature variation exceeding 200.degree. K. Moreover, the mechanical strength characteristics of the filters requires that the heat gradient within them is kept equal to or below 20.degree. K. during the temperature drop.
Furthermore, like the complete satellite, the optical system is exposed to severe mechanical stressing in the form of vibrations, both when it is at 300.degree. K. and when it is at very low temperatures (which can be close to zero K).
Finally, the choice of the fixing device must also take account, in such an application, of the reduced volume allocated to it on the satellite and the need of ensuring a precise and substantially constant positioning of the filters no matter what the temperature, as well as the earthing of the filters or their covering.
A first fixing procedure known in connection with uses at ambient or close to ambient temperature consists of bonding or glueing the filters to their support. However, the widely differing expansion coefficients between the materials of the filters and the support would, in the case of a use at very low temperature, lead to a deformation or fracture of the filters at the point where they are bonded to their supports. This problem was revealed by tests performed at 4.degree. K. on diiferent adhesive or glue groups. In addition, this solution also does not make it possible to ensure the earthing of the filters or their covering.
Another procedure used at ambient temperature, particularly for fixing lenses in objectives, consists of fixing the filters by means of a ring screwed into a support. However, this solution is also not completely satisfactory, because it is incompatible with the application of a high heat gradient and does not make it possible to ensure a constant tightening. Moreover, the use of a screwed ring may lead to the breaking of the filters under the effect of the relative rotation between the ring and the latter during tightening. Moreover, it significantly increases the overall volume.
A third fixing procedure used at temperatures close to ambient temperature consists of bonding the filter to an annular member, which is rendered integral with the support by bending strips, so as to not induce stresses in the filter. However, this solution also fails to deal with the problem of the bond between the filter and the annular member which it supports.
Therefore all these known devices, which are conventionally used at ambient temperature and for fixing not very fragile optical members, cannot be used when they are exposed to high thermal gradients and when the members which they fix are fragile and have physical characteristics evolving with the temperature.